Hybrid ARQ protocols combines a forward-error-correction (FEC) with a retransmission mechanism to provide reliable communication over noisy channels. A packet is only retransmitted if the error-correcting code is not able to correctly decode the packet. To lower the average transmitted amount of redundancy information, type-II hybrid ARQ protocols have been introduced. For the initial transmission, only a small amount of parity information is transmitted with the actual source data. If decoding fails, additional parity information is transmitted incrementally (incremental redundancy, IR) to form lower rate codes. To this end rate compatible codes are often used to allow the construction of a high rate code from a low rate codes by puncturing parts of the parity information. Different error-correcting-codes like Reed-solomon codes, convolutional codes turbo product codes or low-density parity-check (LDPC) code can be used in this scheme.
A general approach to construct rate compatible LDPC codes is disclosed in “A Data Puncturing IR-scheme for Type-II Hybrid ARQ Protocols Using LDPC Codes” in IEEE Communications Society Globecom 2004, page 3012 to 3016, by Uwe Dammer etc. According to the disclosed scheme, incremental redundancy is created from punctured versions of the original data using the same encoder/decoder hardware. If the initial redundancy is not sufficient, only additional parity packets rather than entire packets must be retransmitted and parts of the initially received data can be gradually improved until successful decoding of the entire code is possible. In this way, the data puncturing LDPC obtains a better throughput comparing with other candidate rate compatible codes.
However, data puncturing suffers great performance loss and its adverse impact is more evident as the puncturing rate increases, and in the worst cases, the large percentage of punctured bits may paralyze the iterative soft decision decoder. And furthermore, as other typical transmission schemes using HARQ type-II, the use of rate compatible codes makes the decoding scheme more complicated. All these reduce system transmission performance and thus make the decoder does not work efficiently as originally expected.
Thus there is a need for providing a more efficient transmission scheme for use in a wireless communication system using hybrid ARQ protocol.